1. Field of the Invention
The present invention relates generally to a yarn tensioning apparatus. In one aspect, the present invention relates to a solenoid useful in yarn or filament tensioning devices In a second aspect, the present invention relates to a yarn or filament tensioning device employing such a solenoid. In a third aspect, the present invention relates to an apparatus comprising a plurality of yarn tensioning devices and to systems for controlling the plurality of devices. In a fourth aspect, the present invention relates to devices for determining the tension . exerted on a filament or yarn.
2. Prior Art
A typical yarn tensioning device for tensioning a running length of yarn includes a pair of adjacent confronting yarn engaging members which are forced into engagement with the yarn by means of a solenoid. Generally in textile processing, a large number of such yarn tensioning devices are used together to process many strands of yarn simultaneously.
There is widespread dependence of overall quality in most textile processing on the precision or uniformity of tension of the individual yarn ends. Once yarn tension control is lost or allowed to vary at any point of the process, whether winding, beaming, texturizing, knitting or other fabric formations, it is difficult or impossible to compensate for the quality degeneration. Streaking, barre, off yield, excessive knitting defects, denier variation are familiar problems that frequently have their origin in incorrect or uncontrolled tension on the individual yarn strands.
In order to control the tension on the yarn, it is necessary to have control over the solenoid causing tension to be exerted on the yarn. However, most solenoids are designed to generate the maximum force possible at the end of their stroke. Because the force exerted by the solenoid increases rapidly at the end of its stroke, it is difficult to control the force exerted by the solenoid and the tension applied to the yarn.